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Discussion Starter #1
So I set my tire pressures at 32psi last night for today's autocross in a 68º garage. The tires in question are Bridgstone Ponenza RE71's. It went from 60º on the morning runs to 75º on the afternoon runs. A lot of talking and mumbling back and forth regarding tire pressures in the afternoon. Since I'm not burning rice or driving a Porsche little of the mumbling applied. The 2005+ Mustang crowd, very well represented and kicking butt VS the Chebby guys didn't seem to care in the least about tire pressures that they were willing to share. Don't know were to start on this?
 

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...or use tape so it doesnt look like you were vandalized. Whatever else you might find reading about those tires and pressure add a couple PSIs to it since your car is likely lighter than most others.
 

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Discussion Starter #7
75 and sunny in Merica today! PSA. Don't leave your SPF 100 sunscreen in your work truck over the winter in sub zero conditions and actually expect it to work the next spring.
 

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75 and sunny in Merica today! PSA. Don't leave your SPF 100 sunscreen in your work truck over the winter in sub zero conditions and actually expect it to work the next spring.
55 and rainy in NY but I think we are scheduled for mid 70's and sunny tomorrow ,alas not an autox day just a back to work day. sigh
 

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Isn't a nitrogen fill a lot less temperature dependent? I don't autocross so just askin'.
 

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Discussion Starter #11
I had no visible scrubbing on the sidewalls but the last 2 runs were pathetic. I was not alone in my complaining about the track loosing it. I will definitely try the chalk on the sidewalls. This is a great place to learn stuff!
 

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I assume this applies to open track also?
 

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Isn't a nitrogen fill a lot less temperature dependent? I don't autocross so just askin'.
Not significantly, the important part is to have dry air. Moisture inside the tire will tend to cause a larger increase in pressure. I'm not sure it matters in Autocross, since you can adjust pressures before each run. I wouldn't think pressures build that much during a run ??
 

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When I went to pick up my SHO, they had an up charge on the sticker for nitrogen inflation. I told them I didn't want it, and I wasn't going to pay for it, and they could keep the car. They took the up charge off.
 

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I notice big differences in how my car handles during an autocross day as I get them dialed to the scrub arrows. I used to bring an infared gun and have tried a borrowed temp probe after getting the scrub lines right, the tires were evenly heated. I over inflate slightly at home and bring an air tank. Before my first run, I drop the tires to around 38 up front and 30 out back. Then run and dial from there. I use sidewalk chalk. Usually I'm dialed by the third run but check and re-chalk between every run.
 

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I notice big differences in how my car handles during an autocross day as I get them dialed to the scrub arrows. I used to bring an infared gun and have tried a borrowed temp probe after getting the scrub lines right, the tires were evenly heated. I over inflate slightly at home and bring an air tank. Before my first run, I drop the tires to around 38 up front and 30 out back. Then run and dial from there. I use sidewalk chalk. Usually I'm dialed by the third run but check and re-chalk between every run.
I think I have your chalk BTW
 

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SO to finish this discussion, once you get your tires scrubbling correctly at the arrows then start playing:


TO add Oversteer; Increase front pressure and or decrease rear pressure - vice versa, unless its dramatic, I use 2 lb increments, my personal preference is to get scrubbing all 4 scrubbing right then adjust the rears to dial it in for the conditions of the day and set up for the fastest part of the course e.g. I want to be fast in the fasted part of the course...
 

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Discussion Starter #20
Thanks for the advice everyone. I did notice once I got the car on the lift after the last event that the front tires were at one point in the day scrubbing to the arrows, but almost nothing at the rear. I have a potential autocross this Sunday at a county cop shop/ government center. The same one with the horrible pavement where I snapped my axle. I'll be starting in second gear this time if I go.
 
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